From the author of

From the author of

This article and the second one in this series ("A JNLP Tutorial: Part
2An Example") cover the essentials of the Java Network Launching
Protocol (JNLP). They are intended for a wide audience, mainly developers, and
especially those new to this technology. At the end of this tutorial, you will
have a clearer idea of this Java technology, and hopefully you will be able to
use it directly in your applications.

A Web-Centered Protocol

Our story begins at the end. After your application is finished, you are
ready to install it onto your client machines. This phase is called the software
deployment phase. You should install the proper JRE and copy your JAR files on
the client computers. Now, imagine that you publish all the JAR files on your
Web site. Then, when everything is ready, you send an email to your
customersasking them to point their Web browsers to a given URL. They do
so, and after all needed installations take place automatically (the wanted JRE
and your JAR files, plus all the other resources you need for your Java
application to run), your clients can happily run your program. Then, whenever
you update the JAR files on your Web server (say for the 1.2 release), they are
automatically installed on client machines the next time your software is
launched. So users always have the latest version of your
applicationtransparently to them.

Everything works through the Web browser and the MIME type mechanism. The
very first time users click on your application URL the browser will ask if that
associated plug-in is to be installed. That plug-in is a JRE, with a little
native executable (the JNLP Client) that will manage the whole protocol on your
client's machines. Sun provides this executable freely for the most popular
platforms (it is called Java Web Start) but other vendors and open source
initiatives provide similar software for all the major OS. Starting from the
Java 2 version 1.4 on, it comes included with the standard JRE package.